Collagenous fibroma (desmoplastic fibroblastoma) of the finger in a child.

Collagenous fibroma (desmoplastic fibroblastoma) is a distinctive benign fibrous soft tissue tumor that typically occurs in the subcutaneous tissue or skeletal muscle in adults. We describe a case of collagenous fibroma in a 7-year-old boy who presented with a 1-cm solitary, firm nodule on the volar aspect of the metacarpophalangeal joint of the left little finger. Microscopically, the tumor was composed of spindle- and stellate-shaped cells embedded in a hypovascular, densely collagenous stroma. No mitotic figures, calcifications or necrosis were identified. Immunohistochemically, tumor cells were diffusely positive for vimentin, but negative for smooth muscle actin, muscle-specific actin, desmin, cytokeratin, S-100 protein or CD34. To our knowledge, this is the second reported case of collagenous fibroma in children. Our case report indicates that the clinicopathological features of collagenous fibroma in childhood are similar to those in adults.